Arrangement to control heat flow between a member and its environment

ABSTRACT

An arrangement of insulating, thermal absorbing and/or dissipating elements controlling heat flow between a member and its environment. In certain permafrost environments, for example, one or more elements of the system can include a heat sink and/or a thermal bleed where the member is heated. The arrangement controls heat flow from a heated member at such a rate that the total heat transfer does not exceed the limits of the residual heat capacity of permafrost below the freezing point thereof during cyclic climatic influences. The arrangement takes advantage of the fact that artificial heat from the heated member can be controlled, while natural solar heat is balanced by the seasons. The elements also serve to maintain relatively stable temperature differentials between heated or cryogenic materials and their adjacent ground support, so there is a minimal effect of one on the other.

CROSS REFERENCE TO RELATED APPLICATION

This is a division of application Ser. No. 112,636 filed Feb. 4, 1971,now U.S. Pat. No. 3,768,547, granted Oct. 30, 1973.

This invention concerns an arrangement of elements for controlling heatflow between a member and its environment. For example, there has been aproblem of providing adequate thermal protection for heated members,such as an oil pipeline or building structures, in Arctic regions whereundue melting of the permafrost could have a major impact on thestability of the environment and possibly the security of such heatedmembers. By heated members, or fluids and the like is meant members,fluid, or the like at a temperature greater than that of the adjacentground support. It is known that a heated pipeline, through thermaldissipation, will cause a constant and continuous thawing anddegradation of its adjacent supporting permafrost ground. In theparticular case of an oil pipeline, since support for the pipeline mustfind its foundation within or on such ground, disruption of thepermafrost support can directly result in rupture of the line andspillage of heated oil, or other heated fluids, which might be presentin such a line resulting in even more disruption of the permafrost.Further than this, spillage of such fluids in any significant quantitycan cause untold pollution of the surrounding environment. Where heatedbuildings cause melting of the permafrost, severe settelement of thebuildings due to loss of support can cause undue damage to thestructures.

In some instances, just locating an insulating layer, such as a closedcell plastic foam or its thermal equivalent, between the heated memberand the permafrost, might be adequate if thick enough and in an areawhere the mean annual temperature is very low, as for example 10° F. atthe North slope of Alaska. However, where the heat sink capacity of thesurrounding ground is significantly less than found in this area, suchan insulation layer is not adequate to keep the heated member fromaffecting and deteriorating the permafrost upon which it is supported.

Also found to be a problem has been the excess heat which can begenerated by flow friction of a fluid through a pipeline or the like, itbeing preferable to keep the temperature of the fluid relativelyconstat.

Where cryogenic fluids are carried in a pipeline, or in other cryogenicapplications, yet other problems arise, it being essential that thetemperature of the fluid within the line be affected as little aspossible by the surrounding supporting earth, be it permafrost orotherwise. Fluctuations in the temperature interface between such a lineand its surrounding support can result in many practical problems.

Accordingly, it is among the objects of the present invention to providean arrangement of insulating, thermal absorbing and/or dissipatingelements in the proximity of a heated member which acts as a thermalprotection system for permafrost supporting the heated member. It isanother object to provide such an arrangement which relies on the factthat artificial heat from the heated member can be controlled, andnatural solar heat is balanced by the seasons.

Yet aother object of the present invention is to find a satisfactorysystem for dumping excess heat generated by fluid flow friction. Stillanother object of the present invention is to minimize the effect of thesurrounding environment on cryogenic materials supported within saidenvironment.

Briefly, the present invention contemplates various combinations ofinsulating, thermal absorbing and/or dissipating elements to take careof heated members in environments having varying thawing indexes, as forexample, from the North slope of Alaska having a mean annual temperatureof about 10° F. to Valdez, Alaska, having a mean annual temperature ofabout 32° F. The combination of elements can include plastic foam orequialent insulation adjacent the heated member and, in combinationtherewith, a heat sink and/or a ventilating or thermal absorbing cell,the latter allowing free air passage or its equivalent between otherelements in the system. The heated member, such as a pipeline carryingoil or the like at a temperature significantly above that of theadjacent earth, can be locted below or above the ground and employ thearrangement of insulating, thermal absorbing and/or dissipating elementswhich is contemplated hereby. Combinations of such insulating andthermal absorbing and/or dissipating elements can be used effectively insupporting other heated members, such as heated buildings and the likeon permafrost. Bleeding of excess heat from members can also be affectedby such elements. Such elements can also act to maintain a relativelystable temperature differential between cryogenic materials and thesupporting earth; and generally to control heat flow between a memberand its environment.

Yet additional objects and advantages of the present invention are evenmore apparent when taken in conjunction with the accompanying drawing inwhich like characters of reference designate corresponding material andparts throughout the several views thereof, in which:

FIG. 1 illustrates an underground pipeline, with portions broken away,running through a permafrost region either continuously or only insections where circumstances dictate, and extending left to right froman extremely cold region to a generally milder region;

FIGS. 2-5 illustrate in partially exaggerated cross section variousarrangements of insulating, thermal dissipating and/or absorbingelements for different situations encountered in various permafrostregions taken along lines 2--2 through 5--5 of FIG. 1;

FIG. 6 is a view like FIG. 5 only showing a modified version thereof;

FIG. 7 is a graphical representation of thaw penetration where a sectionlike that of FIG. 3 is employed;

FIG. 8 is a view like FIG. 7 but where a section like that of FIG. 6 isemployed;

FIG. 9 is a modified form of the invention showing in cross-section aheated member located above ground in a permafrost region;

FIG. 10 is an enlarged view of the insulating, thermal dissipatingand/or absorbing elements of FIG. 9;

FIGS. 11 through 14 illustrated in partially exaggerated cross-sectionvarious modified arrangements of the present invention all incorporatinga thermal bleed immediately adjacent a heated member; the portions ofthe core not illustrated for convenience only, but intended to beincluded;

FIG. 15 is a modified form of the invention showing in cross-section abuilding structure as heated member located in a permafrost region;

FIG. 16 is a view like FIG. 15 only showing yet another modified versionof a building structure employing the concepts of the present invention;

FIG. 17 illustrates a partially exaggerated cross-section of anunderground pipeline which pipeline carries a cryogenic fluid and isadapted to be located in adjacent earth which is at a substantialyhigher temperature than that of the cryogenic fluid; and

FIG. 18 is a graphic representation of an interface effect on thepipline of FIG. 17 because of elements of this invention as compared toprior art concepts.

In order to describe the invention in some detail, a specific embodimentthereof is illustrated in FIGS. 1 to 5, which represents an oil pipeline10 extending from the North slope of Alaska having a mean annualtemperature of about 10° F. and an air freezing index of about 8500degree-days each year, to Valdez, Alaska having a means annualtemperature of about 32° F. and an air freezing index of about 3,000degree-days per year. A "degree-day" as used herein represents one daywith a mean air temperature one degree below or above freezing. The"freezing index" merely represents the number of degree days belowfreezing during a year and is commonly used to calculate the depth ofground freezing during the winter. The "thawing index" on the otherhand, is merely the number of degree days above freezing during a year.For example, a freezing index of 10 degre-days may result when the meanair temperature is 31° F. for 10 days or when the mean air temperatureis 22° F. for 1 day.

It should be appreciated that in the following description of thepipeline 10, specific details are shown to describe a preferredembodiment for a particular permafrost region and situation, and thatthe concept of the invention is equally applicable to other permafrostsituations and lines carrying other fluids, gases as well as liquids, attemperatures above the transition temperature of the adjacent earth,about 32° F. or greater, and that the specific details of both thestructure and its location may vary accordingly and still be within theconcept of the invention as claimed. By "permafrost" is generally meantsoil, rock tundra or other ground or earthen material which is frozen inthe winter and which does not completely thaw out during the warmerseasons. Other explanations of permafrost can be found such as in the"Environmental Atlas of Alaska" by P. R. Johnson and C. W. Hartman,published 1969 by Institute of Water Resources, University of Alaska. A"permafrost region" is where permafrost occurs.

In the specific embodiments of FIGS. 1 to 6, 9 and 10 the followingsituation could exist:

a. Pipeline 10 includes standard 48 inches diameter steel oil pipe 12having a 1/2 to 3/4 inch wall thickness;

b. The pipeline is located underground so that the centerline of pipe 12is about 6 feet below surface 13 of the permafrost soil 15;

c. Hot crude oil at a temperature of about 180° F. is the fluid 19carried by the pipe 12.

Referring now more particularly to FIGS. 1 and 2, pipeline section 11comprises pipe 12 surrounded about its circumference by insulation layer17. The insulation layer 17 can be a closed cell urethane foam, or itsfunctional equivalent, having a k factor of about 0.24 BTU/ft²/hr/°F/in. thk., and is about 4 inches in thickness. For example, astyrene maleic anhydride foam could be used as it has good solventresistance to hydrocarbons. The environment for which this pipeline isadapted can be one such as is found on the North slope of Alaska whereinthere is a mean annual temperature of about 10° F., the air freezingindex being approximately 8500 degree-days each year, and the airthawing index being about only 500 degree-days per year. Since in thislocation the conductance and volumetric heat capacity of the permafrostbelow the thawing temperature is so large insulation of the typedescribed is adequate to prevent any significant disruption of thepermafrost layer due to the heat dissipated from the hot oil 19 in thepipeline through the insulation layer 17. However, even in this region,if the water content of the soil is too great, and/or does not havesufficient structural integrity it may be necessary to employ a pipelinesection 16 as described hereinafter.

Heat absorbing and/or dissipating elements are added to the insulationsystem, as shown in pipeline section 16 of FIG. 3, to meet conditionsfound in Alaska south of the North slope as, for example, at the 66° N.Latitude which has a mean annual temperature of about 15° F. Here theair freezing index is somewhere between 6500 to 7000 degree-days F. andthe air thawing index is around 2500 degree-days F. The pipeline section16 is the same as that pipeline section 11 previously described onlywith a closed annulus heat sink in the form of a thermocell or heat sink18 being located about insulation layer 17. The thermocell can comprisevarious configurations for contaning or enveloping a heat sink material.The embodiment of thermocell 18 comprises inner and outer cylindricalskins 20 secured on opposite nodular ends of a core structure 22; whichcore structure, for example, can have a shape such as that shown in U.S.Pat. No. 3,277,598. The core structure primarily is one which separatesthe two skins and permits of fluid flow therethrough and, as such, canalso be of bent corrugated metal, a granular or other particulate fillor other configurations and various materials such as also taught inU.S. Pat. No. 3,086,899 and 3,190,142, for example. The membercontaining the heat sink material should have sufficient impermeabilityto contain the heat sink material in its fluid state so thatsubstatially none is lost in such state. The skins 20 can be adhered byadhesives, welded, heat sealed, or otherwise secured with the core 22.The thermocell can be made of a plastic material such as polyethylene orrubber modified polystyrene, but can be formed of other polymeric,metallic, organic or other synthetic or natural substances havingsufficeint strength and impermeability to satisfy the requirements ofsuch a thermocell. A liquid 24 enclosed within the thermocell 18 can bea saline, glycol or other solution sufficient to give the thermocellheat sink a freezing point slightly less than the transition temperatureof the surrounding permafrost (usually about 32° F.) as, for example,30° F.

The liquid 24 incorporates a freezing point suppressant in water that insolution acts in a eutectic manner in the range of temperatures below32° F. One such material can be a frozen solution containing less than5% sodium sulfate. Specifically, a 3.84% solution by weight of sodiumsulfate in water has a freezing point of approximately 30° F. Likewise,a 1% propylene glycol solution, by weight, has a freezing point ofapproximately 30° F. When the liquid is frozen, the heat required tomelt the solution is great. The total heat of fusion of the sodiumsulfate solution, for example, is available within a few degrees below32° F., thus, allowing reverse cycling of heat flow at less than 32° F.but stopping heat flow at heat source temperatures above 32° F. The heatsink in this particular instance had a thickness of about twelve inchesfrom skin to skin and is substantially filled with liquid 24. Indesigning the thermocell 18 care should be taken to allow for expansionand contraction of the liquid 24 as the temperature changes.

The presence of the heat sink 18 substantially eliminates flucuations ofthe heat loss from the pipe 12. Thus, the underground pipeline 16 iskept in a near constant temperature environment thereby reducing theexpansion and contraction effects, and therefore the need for expansionand contraction joints in the pipeline.

The presence of the heat sink around an insulated pipe buried inpermafrost will increase the amount of heat transferred from the pipe tothe soil over a 1 year cycle. By controlling the heat transfer from thepipe to the soil such that the permafrost is not thawed, the availableseasonal low temperature of the air during the winter cycle is moreeffectively utilized. The sink system keeps the permafrost in the frozenstate throughout the year and the latent heat of fusion of the water inthe soil is not required. The heat exchange between the pipe and theatmospheric air is maximized since the permafrost is not allowed to gothrough the thawing and freezing cycle. The net result is that theaverage effective temperature differential is greater, therefore moreheat can be dissipated.

For a milder area such as might be found at Fairbanks, Alaska, forexample, which has a mean annual temperature of about 25° F., a modifiedinsulated pipe section 26 such as shown in FIG. 4 can be employed. Herethe freezing index is about 5500 degree-days F. and the thawing index isabout 3000 degree-days F. The insulated pipe section 26 is like the pipeline section 16 only in between the insulation layer 17 and thethermocell 18 is formed a ventilating annulus or thermal bleed 28 topermit air circulation between the two. Since the amount of thawingwhich the permafrost experiences is greater here than at the colderlatitudes, the thermocell 18 need not be designed so that it alone isadequate to prevent significant thawing of the adjacent permafrost soildue to the hot oil 19 in the pipe line 10. Of course, one could increasethe size of the thermocell to satisfy the additional demands made by thewarmer climate. However, it is found more effective, practical andeconomical to provide ventilation in the form of air duct or annulus 27.This is not to say, however, that air is the only method that can beused to transfer the heat flow through the insulation layer to theatmosphere, as will be seen in the modifiction of FIG. 6 describedhereinafter. To take additional heat from the pipe section 26 out to theatmosphere and to ease the load upon the thermocell 18, the annulus 28can have a structure not unlike that of the thermocell 18, that is,having skins 25 like skins 20 and core structure 27 like core structure22 secured together in a similar manner, only at one end thereof,preferably the upper end so as to have the least effect on the soil,providing an inlet 30 and outlet 32, which can be reversed from thatshown, whereby air from the atmosphere can have passage therethrough. Incertain integral constructions, it may be possible for the thermocell 18and annulus 28 to share a common skin. The core is designed so thatthrough passageways are a natural result of construction. It has beenfound that a bleed off of this nature can remove from about 50 to 100BTUs per hour per lineal foot of pipe section 26 located at Fairbanks,Alaska.

During the summer there is the natural flow of heat from the adjacentsoil to thermocell 18 which means the thermocell 18 will have to haveenough capacity to absorb this heat and store it while remaining at 30°F. and therefore not effect the permafrost in the adjacent area.Thermocell 18 also has to have enough capacity to handle warm air comingthrough annulus 28. In permafrost regions the heat absorbed by thethermocell 18 during the summer can be dissipated during the winter. Inthe winter the annulus 28 is removing heat from the thermocell 18 aswell as from heat passing through insulation layers from the pipe.Likewise in the winter, the thermocell 18 is losing heat through thesoil to the atmosphere. Thus thermocell 18 is primarily needed for thesummer months to store both the artificial heat from the pipeline andnatural solar heat at 32° F. or less until such heat can be dissipatedduring the winter months.

In achieving stabilization of the permafrost the invention thus takesinto account both artificial heat, i.e., the heat from the product beingcarried in the pipeline, and natural heat, i.e., solar radiationpenetrating the soil. It recognizes that artificial heat can becontrolled. That is, one can insulate the heated pipe and can use a heatsink or a ventilating or radiating annulus to absorb and dissipate theartificial heat until the atmospheric temperature cools enough, at whichtime the accumulated heat can be dumped. The arrangement also recognizesthat the natural heat source is balanced by the seasons. Thus, thenatural heat source varies between hot (generally above 32° F.) and cold(generally 32° F. or less) while the artificial heat source iscontinuously hot. Natural heat source thaws from the top of thepermafrost soil downward while the artificial heat source thaws fromwithin the permafrost outward. In accomplishing stabilization of thepermafrost the invention uses both energy absorption and energytransfer. It is thus recognized that the entire job for a greatlyvarying permafrost region cannot be satisfactorily accomplished withinsulation alone or even necessarily together with a heat sink at alllocations. But with a combination of these elements, together with addedelements, such as an annulus, where necessary a practical balanceproviding a protective arrangement in all permafrost regions isachieved. This is further exemplified by the other sections describedhereinafter.

At warmer locations, as for example, as found at 64° N. latitude inAlaska where there is a mean annual temperature of about 27° F. with afreezing index of about 4000 to 4500 degree-days F. and a thawing indexof about 3000 degree-days F., more insulation is required as illustratedfor the pipeline section 34 of FIG. 5. Pipeline section 34 is likepreviously described pipeline section 26 only with an added insulatingfoam layer 36 about the outer circumference of the thermocell 18, theinsulation layer 36 being of the same type and having properties likethat of the insulation layer 17. This is a preferred combination ofinsulation and heat dissipating elements to prevent significant thawingof permafrost in an economical structure of this somewhat milderpermafrost region.

Pipeline section 34 functions in the same manner as pipeline 26, butinstead of having a thermocell forming a heat sink of a depressedtemperature solution such as a glycol solution at 30° F. it includes,alternatively and optionally, a heat sink filled with water, therebyhaving a freezing point temperature of about 32° F. In this type ofarrangement an insulation layer 36 is provided between the permafrostand the thermocell thereby reducing the interface temperature betweenthe permafrost soil and the system. Otherwise, a direct interfacerelationship between the thermocell and the permafrost soil would resultin some melting of the adjacent permafrost soil which, over the years,could result in settling of the pipeline. The temperature drop throughthe insulation layer 36 reduces the interface temperature between theinsulation layer 36 and permafrost soil 15 to less than 32° F. Theinsulation layer 36 may, in the winter time, slow down the dissipationof heat from the thermocell but this is not a great amount and is morethan compensated by the fact that during the summer the heat flow fromthe natural environment is slowed to the thermocell 18.

Where the situation changes to one having a mean annual temperature ofabou 32° F., wherein the thawing index is substantially greater than thefreezing index as, for example, at Valdez, Alaska, where the thawingindex is about 30000 degree-days and the freezing index is only about1500 degree-days, one can use a simple pipe insulation arrangement asshown for pipe section 11 in FIG. 2. The insulation in this instance,however, is for the opposite effect than that earlier described for thesoil in this location is not permafrost. Here the insulation serves onlyto prevent the oil from cooling too significantly during the winter andcausing significant desiccation and other variations in the adjacentsoil.

So at both extremes of temperature, from that experienced, for example,at the North slope of Alaska to the Southern tip of Alaska, andcorresponding other places of the world, such as found in Canada andSiberia and even certain latitudes in Japan and the United States, byapplying combinations of insulated pipelines sections taught here,damage to the adjacent soil and to the pipeline can be prevented nomatter what the weather.

In the embodiment of FIG. 5 a section 35 of insulation layer 17 canoptionally be removed from adjacent the pipe 12 so that a hot spot isformed. This hot spot will accelerate the flow of cooling fluid, in thiscase air, about the annulus since it will be substnatially warmer thanthe air from the atmosphere flowing through the annulus. The widedifference in temperature between the hot spot and the atmospheric airthus greatly accelerates heat dissipation. The hot spot however, is notso large to exceed the capacity of the thermocell 18 adjacent thereto toabsorb the heat escaping therefrom. This is an optional advantage whichcan be included where circumstances permit. Alternatively, a high heatconductive material (not shown), such as steel or aluminum could belocated in open section 35 and extend upwardly adjacent the groundsurface. By conductance the heat would flow through the pipe wall intothe high conductance material acting as a thermal bleed dissipating theheat near the surface of the ground. To control where the major heatdissipation takes place, the high conductance material can be insulatedsuch that the major heat loss takes place in the active surface layer ofearth above the pipeline.

A variation of pipeline section 36 is that illustrated as section 40 inFIG. 6. One of the chief differences is that the outer layer comprisingouter layers 42a and 42b are much like insulating layer 36 previouslydescribed, thermocell 44a and 44b are much like thermocell 18 previouslydescribed, and thermal bleed or ventilating annulus 46a and 46b,somewhat different from previously described annulus 28, are all bundledtogether in half cell units for ease of manufacture and installation.Since each of the half sections can be easily clamped, adhesivelyfastened or otherwise secured to each side of the pipe 12, each can bereadily installed in the field as composite units of easily handledlengths and secured around the pipe 12 therealong. The insulation layer17 remains the same as the previously described and is either formedabout the pipe in the field or prior to assembly of the pipe itself inthe same manner as for pipe section 11.

Ventilating annulus 46a and 46b differs from those previously describedin that this is a closed heat dissipating systems so therefore can belocated entirely underground and can generally give better control sinceit is not subject to as great an extent to short term fluctuations inoutside ambient temperatures. Annulus 46a and 46b can be filled with aparticular saline or glycol solution 48, or its equivalent, which willnot freeze at a desired temperature below 32° F. The internalcirculation is dependent upon the thermal density change of the heattransfer media within the annulus. The core 45 of the annulus, ofcourse, divides the annulus into inner and outer sections 47 and 49,respectively, and the flow of the heat transfer media, fluid 48, isalong one side and back along the other side of the core. To facilitatethis flow the core 45 should be perforated at either end or can be cutshort on each end to permit flow about either end of the annulus 46a and46b. During the winter, since the hotter part is adjacent the insulationlayer 17, the media on this side (inside section 47) flows towards thetop of the annulus section where, when it reaches ears 50a and 50b whichare exposed to the cold permafrost soil 15, it is thereby densified, andthen flows downwardly along outside section 49 past the thermocell andremoves heat from the thermocell thereby regenerating its heat capacityfor use in the summer. Since in the summer the density of fluid 48 isnot increased at the ears 50 because of the warmer soil, flowsubstantially stops and therefore heat from the surface is not carriedto the thermocell 44a and 44b.

To illustrate the actual effect of using the present invention in apermafrost region where a pipe section 16 such as that shown in FIG. 3is employed under the following conditions and taking effect for theartificial constant heat produced by hot oil in the pipe and thevariations due to the climatic natural solar heat or lack thereof duringthe various seasons of the year, the data being as set forthhereinbelow, the conditions were found by computer to be as shown inFIG. 7:

    ______________________________________                                        Climatology Data                                                               Annual Mean Average Temperature                                                                        12° F                                        Physical Data                                                                  Pipe Diameter            4'-0"                                                Crude Oil Temperature    180° F.                                       Depth of Burial--to centerline of pipe                                                                 6'-0"                                                Insulation thickness     6"                                                    "K" factor - 0.24 BTU/ft.sup.2 /hr/° F/in. thk.                       Heat sink       12" thk, annulus                                               30° F. freezing point                                                Soil Data                                                                      Thermal Diffusivity. -  Melted                                                                         0.023 ft.sup.2 /hr.                                   Frozen                  0.046 ft.sup.2 /hr.                                  Latent Heat              21.6 BTU/lb                                          Density                  118.6 bls/ft.sup.3                                   Soil Surface Temperature (T)                                                   Variation with time (t) in days                                                         2 π t                                                          T = 12 + 36 Sin (  - 2.0)                                                                 365                                                               ______________________________________                                    

The shaded areas, substantially the transverse darkened area at or nearthe top at each graphical representation, is the part of the soil whichis at or above 32° F. for the particular period covered. Thenon-darkened areas of permafront soil 15 is all below 32° F. Therepresentations cover the months of June through November, for these arethe only months in which it was found that thawing occurred. In themonths Decemeber through May, it was found there was no thawed zone, thesoil being completely frozen. As the summer progresses from June throughSeptember, the degree of thawing becomes greater. Then in October it wasfound that there is a double front wherein the thawed area is squeezedfrom both the top and the bottom since the colder air is cooling thesurface 13 to a temperature below 32° F. The double front advances onthe thawed area even more in November and in December completelyeliminates the thawed area. It is quite evident from the representationsof FIG. 9 that the effect of the heat from oil pipeline 10 on the soilin the area immediately adjacent the pipeline 10 is minimal at most andat no time was there found to be any noticeable thawing in the soil areaimmediately about the circumference of the pipe section 16.

In a more mild climatic condition where a thawing condition existssomewhere in the permafrost soil throughout the year, graphicalrepresentations of the effect of pipe section 26 as shown in FIG. 6,were found by computer to be as depicted in FIG. 8 with pertinent databeing as follows:

    ______________________________________                                        Climatology Data                                                               Annual Mean Average Temperature                                                                        30.6° F.                                     Physical Data                                                                  Pipe Diameter            4'-0"                                                Crude Oil Temperature    180° F.                                       Depth of Burial--to centerline of pipe                                                                 7'-0"                                                Insulation thickness     6"                                                    "K" factor - 0.24 BTU/ft.sup.2 hr/° F./in. thk.                       Heat sink       24" thk. annulus                                               31° F. Freezing Point                                                Soil Data                                                                      Thermal Diffusivity                                                            Melted                  0.023 ft.sup.2 /hr.                                   Frozen                  0.046 ft.sup.2 /hr.                                  Latent Heat              21.6 BTU/lb                                          Density                  118.6 lbs/ft.sup.3                                  Soil Surface Temperature (T)                                                   Variation with Time (t) in days                                                             2 π t                                                       T = 30.6° F. + 36 Sin (                                                                      - 1.8)                                                                 365                                                            ______________________________________                                    

Since there are thawed areas in the representations throughout theentire year the annual period is covered by FIG. 8 and the advance andthe retreat of the thawed area in this case shown for every 2 monthperiod, intermediate months generally showing a condition between themonths on either side of it. The double front situation where the coldambient air temperature is causing the freezing front to progressdownwardly from the soil surface 13 to freeze and diminsih the thawedarea is shown by the January representation. As the winter progressesthrough March, the thawed area immediately adjacent the pipesubstantially disappears and the other thawed areas are substantiallydiminished. Then as warmer weather comes along, as shown in the Mayrepresentation, thawing from soil surface 13 again commences and thethawed area becomes progressively greater until colder weather againsets in as shown in the November representation and the double frontcondition starts anew. Again there is substantially no thawing of thepermafrost immediately adjacent the pipe section 40 except at the verytop thereof near the end of the warmer season where the thawed areanormally progresses to the depth of the pipe section anyway. Again, itis quite clear from this representation that hot oil carried in the pipeline section has no adverse effect on the permafrost condition on thesoil in which it is located.

While the present invention finds unique and extremely advantageousapplications in an underground pipe line system some of its concepts mayalso be applied, with modification, to an above ground pipe line system,an example of which is shown in FIGS. 9 and 10. The pipe line 52includes a pipe 54 carrying a fluid 56 above 32° F. and has aninsulation cover 58. The pipe 54 is like the pipe 12, and the insulationcover 58 is like the insulation layer 17, previously described. In thiscase the pipe 54 is carried on a saddle 60 which has to be sufficient tocarry the full weight of such a pipe section. The total weight of such apipe and the oil therein would total about 1,250 lbs. per lineal foot ofthe pipe line 52. The pipe saddle 60 is carried on an insulation andheat absorbing and/or dissipating section 64 which includes an air duct66, an insulation layer 68 and a thermocell heat sink 70, the details ofwhich are better seen in FIG. 10. The entire pipe line supportingsection 64 is located in a gravel bed 72 which acts as a leveling layerand rests upon the permafrost soil 74.

Referring now more particularly to FIG. 10, pipe saddle 60 can besupported on a bearing surface layer 76 such as might be formed from ahigh density polyethylene plastic material to permit some shiftingbetween the saddle 60 and supporting section 64, due to subtle shifts ofthe soil and otherwise, without disturbing the disposition of the pipeline 52. The air duct 66 has a core 78 and skins 80 substantially likethose shown for the thermocell 18 of FIG. 4 only laid out flat. Foaminsulation layer 68 can be formed of the same material as the insulationlayer 18 of FIG. 4 only laid out flat. One such insulation material canbe closed cell polystyrene foam, like Styrofoam brand expandedpolystyrene produced by The Dow Chemical Company. In thermocell 70, thecore 84, skins 86 and fluid 90 are like the corresponding core 22, skins20 and fluid 24 shown in FIG. 4 all of which components are flat ratherthan curved but function in like manner. In the winter time the cold airpassing through the duct 66 keeps heat from the pipe away the permafrostsoil 74. In the summer, the insulation layer 68 protects the permafrostsoil 74 from the heat generated by both the pipeline 52 and from thesolar heat. Thermocell 70 inthe summertime stores heat that passesthrough the insulation layer 68 preventing such heat from going throughthe gravel layer 72 and into the permafrost soil 74. During the wintermonths, of course, the thermocell 70 is regenrated and heat is removeddue to the cold air moving through the air duct 66 and the generallycold conditions in the surrounding atmosphere.

In some instances where a heated material flow through a pipeline or thelike, such as heated oil traveling through the line, the flow frictiongenerated by the passage of the liquid increases the temperature of thealready heated fluid. For example, heated oil which initially enters thepipeline well above 32° F. may be increased in temperature by severaldegrees in traveling just a relatively short distance through the line.Since it is desirable to maintain the oil at a constant temperature sothat proper flow is obtained, no phase change occurs and the metal ofthe pipe is not subjected to unwanted temperature variations, it istherefore a desirable objective to dump the excess heat generated by theflow friction to the atmosphere.

In a zone where there is earth which is not particularly disturbed byincreases in its temperature, it has been found possible to accomplishthe immediately preceeding desired objective by employing a thermalbleed only about the periphery of such a pipeline, as illustrated inFIG. 11, buried, supported on rock or otherwise located adjacent suchsubstantially non-heat effected earth. Here in section 90, pipeline 12carries a fluid 19, usually at a temperature above 32° F., when flowing,and is surrounded around its periphery by a thermal bleed 92. Thermalbleed 92 is preferably like in structure, with skins and core providingdual internal passageways, to the thermal bleed 46A and 46B previouslydescribed with respect to FIG. 6, and includes ears 94 to dissipate theheat to the surrounding earth and/or atmosphere. The fluid 93 (likeliquid 24) within the thermal bleed 92 flows upwardly along thepassageway of the core, which can be insulated, adjacent the heatedpipeline 19 and back downwardly along the passageway outside of the coreas it cools in a manner not unlike the previously described but in thiscase for the primary purpose of dumping the excess heat generated byflow friction of the fluid with the pipeline, but also to reduce thetemperature of fluid 19 when desired. The freezing point of the fluid 93can be selected so that its freezing point is not below the temperatureat which the fluid 19 will effectively commence flowing, in the eventthe line shuts down and the fluid 19 becomes cooled.

Modified section 95 of FIG. 12 is like FIG. 11 only includes a blanketof insulation 96 like layer 17 previously described, about the thermalbleed 92. This section 95, as are the following sections 100 and 104 ofFIGS. 13 and 14 are particularly adapted for permafrost regions whereheat can disturb the permafrost support. The particular permafrostregion for which the structure of FIG. 12 is adapted is for that wherethere is extremely cold prolonged winter seasons such as thatexperienced near the North slope of Alaska. The thermal bleed 92 in thiscase again provides for maintenance of the oil at a desirabletemperature, by permitting bleed-off of the excess heat occasioned byflow friction. With the insulation 96 there is created freezing pointinterface between the pipeline 12 and the permafrost such that there issubstantially no melting of the permafrost. Again this is onlyapplicable where the freezing conditions are extreme and the permafrosttherefore has an especially high heat sink capacity, to absorb any flowthrough of heat through the insulation.

In a location where the winter season is not so severe such that theheat sink capacity of the permafrost is less than that desirable for thesection 95, the section 100 of FIG. 13 is recommended. The functions ofcomparable elements of section 100 are like those of section FIG. 12,and like components have like reference numerals. In addition, a heatsink or thermocell 102, is employed to absorb excess heat which may comethrough the insulation layer 96. The termocell 102 stores this heatuntil the wintertime when it is transmitted through the permafrost intothe atmosphere. The structure and components of thermocell 102 can bethe same as those of the thermocell 18. Again, the thermal bleed 92 actsto remove excess heat from the fluid 19 to maintain it at the desiredtemperature.

Section 104 illustrated in FIG. 14 includes heat sink thermocell 106,thermal bleed 108 and insulation layer 110 which are comparablerespectively to thermocell 18, thermal bleed 28 and insulation layer 17of section 26 of FIG. 4 respectively; with the exception that there isalso included a thermal bleed 112 between the insulation layer 110 andpipe 12, and the insulation layer has extensions 111separating the upperportions of the two thermal bleeds. The function of the thermal bleed112 as shown in FIG. 14, is to remove excess heat from the pipe, whichmay be generated from the friction due to the fluid flow so as tomaintain the heated product 19 at the desired temperature. This section104 is therefor adapted to the same general situation as the section 26,but where the heat generated by friction is especially above desiredlevels. The thermal bleed 92 works year around to remove heat from thefluid 19, but the thermal bleed 108 works principally only in the wintermonths to accomplish regenration of the thermocell 106. In the winterthe thermocell 106 therefore readily dumps its excess heat into thethermally active soil layer thereabove and thus to the atmospherethrough ears 109 of thermal bleed 108 so that the amount of excess heatdumped into the adjacent permafrost is within its capacity then toreceive the heat without melting. Because of this difference in functionit is best to maintain the thermal bleeds 108 and 112 insulated from oneanother as by extension 111 between ears 94 and 109. Thus the presentinvention can provide for dumping of the excess heat of the heated fluid19 in a pipeline or the like and protect the permafrost simultaneously.

Another source of generally constant heat which can affect permafrostsupport is that which is encountered in heated buildings and the like.When a building is built over permafrost and, although insulated underthe footings and floors, the lack of 100% insulation efficiency allowsheat to flow to the permafrost causing melting, and settlement of thebuilding. The basic problem is that the area covered by the building isno longer subject to the cyclic climatic conditions and the subsurfaceof the ground is not refrozen during the winter period. A typical methodof construction used at the present time is to build the building onpiling leaving an air space below the building. This method, however,has its drawbacks. One is boring the holes in the permafrost to set thepiles in and secondly the piles are jacked out of the ground causing thebuilding to tilt. The jacking is caused by the cyclic temperaturevariations whereby freezing and thawing of the subsurface takes placecausing a vertical thrust movement on the piling. While often such heaveis minimized by the depth of embedment of the pile in the permafrost,oftentimes this is not achieved. There are so many variables thatresults are very uncertain.

The present invention provides a way of building such structures withoutusing piling and yet takes advantage of the cyclical climatic conditionsto refreeze the subsoil under a building following a summer thaw. Oneembodiment of the present invention is that illustrated in FIG. 15wherein a building 120 is located on a foundation slab 122 which can becomprised of concrete or the like. Underneath the slab 122 is aninsulation layer 124 which can be comprised of the same materials asinsulation layer 68 of FIGS. 9 and 10. Below insulation layer 124 is athermobleed or air duct 126 which can be constructed just like the airduct 66 in FIGS. 9 and 10, and permit passage both ways therethrough todissipate heat which may pass through the insulation layer 124.Preferably located below the thermal bleed 126 is ground insulationlayer 128 which layer can be substantially like the layer 124. Below theinsulation layer 128 can be located a heat sink or thermocell 130 whichis substantially like thermocell 70 of FIGS. 9 and 10. The entirefoundation section comprising a section of slab 122 through thermocell130 preferably rests upon a gravel layer 132 or its equivalent, which inturn is supported upon permafrost 134.

In opertion, the foundation of FIG. 15 operates much like pipe saddlesupport section 64. By interposing of thermal bleed 126 between the twoinsulation layers 124 and 128 of a properly selected thermal resistance,the heat flow to the permafrost 134 is controlled such that thepermafrost does not melt. The air flow throughout the thermal bleed 126under winter climatic conditions removes the heat flow through the floorinsulation 124 as well as removing the heat from the permafrost heatsink. The winter cycle, being of longer duration than the summer cycle,has ample time to refreeze and supercool the permafrost soil. Thus, theheat thermal cell 130 is reestablished and ready for the next summercycle.

For example, if the insulation layer 128 is selected such that thermalresistance allows from one BTU to two BTU heat flow per square foot perhour during a summer climatic cycle of 135 days, this heat can beabsorbed in 22 to 44 pounds of sodium sulfate solution or its equivalentin thermocell 130. This is based just on the heat of fusion of thesolution at 144 BTU per pound at 29° F., neglecting any latent heat andvolumetric heat available in the permafrost 134.

Yet another embodiment of the present invention is illustrated in FIG.16 which is also adapted for a much larger heated building or otherstructure, perhaps an oil well production platform, which presentsgreater heat flow problems than that comprehended for the modificationof FIG. 15. The foundation 138, while it can be like something else canalso be much like the foundation 122. Other like reference charactershave been used to designate similar portions between FIGS. 15 and 16.The main difference here is the substitution of two phase thermal bleed140 for the simpler air duct thermal bleed 126. Thermal bleed 140 can bebuilt like thermal cell 130 but is filled with a two phase heat transferfluid 141, like a methyl bromide/methyl chloride mixture solution,having a boiling point, for example, of 20° F. to 32° F. at 760 mm. ofmercury. Other suitable fluids for use in the present invention arematerials such as dichlorodifluoromethane, sulfur dioxide,ethylchloride, trichlorofluoromethane, a 1:1 mixture of methyl bromideand methylchloride. Beneficially be employing such liquids the pressurewithin the thermal bleed can be maintained from about 5-25 pounds persquare inch absolute and pressure equipment avoided. This fluid can befilled to about half the level of thermal bleed 140. The thermal bleed140 is connected via a tubular system 141 with a heat exchanger 142 byan upper flow passage 144 in open communication with the uppernon-liquid part of thermal bleed 140 and by lower passageway 146 in opencommunication with the lower fluid filled portion of thermal bleed 140for return of the condensed fluid. The heat exchanger is filled abouttubular system 141 with a heat sink solution 143 which solution shouldhave a freezing (phase change) point below the boiling point of twophase heat transfer fluid, or with cryogenic liquid or fluid cooled bymechanical refrigeration. Extending out from heat exchanger 142 arecondenser elements 148 in open communication with tubular system 141. Anoptional heat exchanger bypass line 145 can be used for winteroperations, by operation of a two-way valve. In order to maintain apressure system no greater than one atmosphere, a vent 150 forexhausting gases from tubular system 141 can form part of the condensersystem 148 so the components need not be designed to take high pressureswithout failure.

The two phase fluid 14 in the thermal bleed 140 boils at a temperaturegreater than that of the heat exchanger 142 so that when solar heat isabsorbed the phase changes and the gas passes through passage 144 to theheat exchanger 142 in the summer months. Since the heat sink solution143 has a phase change temperature, solid to liquid, lower than theboiled off gas, heat is absorbed from the gas with the result that thegas condenses and returns to the thermal bleed as a liquid. The heatexchanger thus works as a condenser during the summer months. During thewinter months the gas passes through the heat exchanger into thecondenser elements 148 where the cold air around the condenser elements148 absorbs heat from the gas, resulting in condensation of the gas andits return to the thermal bleed 140 via passageway 146.

The present invention also comprehends the carrying of cryogenic liquidsor gaseous liquids, such as a liquified natural gas which can havetemperatures from, for example,, -50° to -300° F. to maintain theirliquified or semi-liquified state for high volume rapid transport.Application of the concept as applied to cryogenics can be that, forexample, where a gas 159 such as liquid nitrogen is transported throughan underground pipeline. Such a pipeline adapted according to thisinvention for carrying such cryogenic materials is represented bysection 160 of FIG. 17 wherein as a specific example, a metallic pipe162 (like pipe 12 of FIG. 2) only having a radius of 1-1/2 ft. caninclude 5-1/4 in. insulating layer 164 (like the layer 17 of FIG. 2) athermocell or heat sink 166 (like the heat sink 24 in FIG. 3) and a 3in. insulation layer 168 (like layer 36 in FIG. 5) which pipe sectioncan likewise be located at a depth of about 6 feet from the surface ofthe ground to the centerline of the pipe 162.

This application of the invention to cryogenics is particularlyadaptable to permafrost regions but is not limited thereto because theliquification temperature for most gases which could be involved is solow, like -256° for nitrogen gas, that whether the soil is below 32° orabove does not involve more than altering the capacity of the system toachieve the desired end. That desired end is to maintain a constanttemperature difference at the interface between the insulation layer 164and the thermocell 166. Were there only an insulation layer ofreasonable thickness about the pipeline the temperature differencebetween the liquiified gas and the outside of the insulation layer wouldbe cyclical, depending on the climatic heat gain or loss in thesurrounding ground areas. For a cryogenic pipeline it is necessary toperiodically bring the gas above ground for refrigeration and repump thegas into the line to maintain the liquification temperature. Thus, whenthe gas begins to approach that temperature, it is again refrigerated toseveral degrees below the liquification temperatures. The prior artpipelines have been designed for the maximum heat exchange in such adesign as represented by the sinusoidal curve 168 indicated in FIG. 18,reflecting the seasonal variations in temperature. By so designing forthe maximum condition, the pipe also has to be capable of withstandingthe minimum condition which can result in the use of especiallyexpensive materials so that brittleness of the material does not cause afailure at the minimum condition. Also with the sinusoidal effect thepipe is subject to constant expansion and contraction which requiresmore expensive pipe, or there can be a high risk of pipe failure.

By the present invention the sinusoidal effect can be dampered to asubstantially straight line effect such as illustrated by thesubstantially straight line 170 in FIG. 18. Thus, the relativedifference between the liquid and its interface with its exteriorenvironment can be constant as, for example, the heat sink can bedesigned to about -60° F. (or some other reasonable temperature whichcan be selected from suitable eutectic solution) for liquid nitrogenwhich should be kept at temperatures of about -256° F. or lower. Overdesigning and relatively expensive material are thus aleviated and thepumping and refrigeration stations can be spaced a greater distance fromone another by maintaining such a constant difference. For example, witha pipeline as shown and described with respect to FIG. 17 wherein the Kfactor of the insulation is 0.24 BTU/hr/sq.ft/degree F./inch thickness,and the following other conditions are present:

    Surface temperature = 40° F. + 30 sin (2τt/365 - 1.8)

Heat sink temperature = -60° F.

Pipe temperature = -256°F.

Thermal conductivity of soil = 0.822 BTU/hr.ft° F.

Heat capacity of soil = 0.3 BTU/lb.° F.

Density of soil = 118.6 lb/ft.³

Capacity of heat sink = 5.6 × 10⁴ BTU/ft.

It has been determined by mathematical analysis that there is a constantflow from the pipe to the heat sink of 93.8 BTU per hour per foot ofpipe while there is a sinusoidal transfer of heat from the ground to theheat sink with a net flow of 5.6 × 10⁴ BTU per foot of pipe over aperiod of 1 year. A similar pipe having only a layer of about 9 in. oflike insulation therearound would have on the other hand a maximumvariation throughout the year of 37 BTU per hour per foot of pipe(approximately 95 to 132 BTU difference) as compared to the constant93.8 BTU present with this particular embodiment of the presentinvention.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope of the invention.For example, various combinations of heat sink, insulation layers,and/or thermal bleed elements described hereinabove can satisfy specialapplications not specifically mentioned above and still come within thescope of this invention as claimed. Likewise, the elements hereof cantake different shapes or parts of shapes or involve other components orcombinations of components other than as specifically described in thepreferred embodiments hereof. Specifically, the elements might extendonly partially between the member and the environment and non-frostsusceptible granular or other material might be employed adjacent theremaining portions of said member in appropriate circumstances.Additionally, the lines might have various other uses than as abovementioned, as for example, carrying utilities such as electric ortelephone cables where it is desired to maintain a relatively stabletemperature within the lines despite the environment.

Accordingly, what is claimed is:
 1. A method for preventing thawing of apermafrost earthen support for a member heated to a temperature greaterthan the transition temperature of said permafrost comprising the stepsof locating insulating material and a heat sink between said member andearthen support, said heat sink comprised of a thermocell which hasspaced skins and a fluid contained therebetween, said fluid having afreezing point no greater than the transition temperature of saidpermafrost, selecting said thermocell such that it has sufficient heatsink capacity that it will not reach a temperature as great as thetransition temperature of the adjacent permafrost, said insulatingmaterial and heat sink preventing thawing of said permafrost which wouldotherwise occur due to the presence of said heated member.
 2. A methodfor preventing thawing of a permafrost earthen support for a memberheated to a temperature greater than the transition temperature of saidpermafrost comprising the steps of locating insulating material and aheat sink between said member and earthen support, said heat sinkcomprised of a thermocell which has spaced skins and a fluid containedtherebetween, said fluid having a freezing point no greater than thetransition temperature of said permafrost, locting a heat dissipatingthermal bleed between said member and said earthen support, saidinsulating material, heat sink and thermal bleed preventing thawing ofsaid permafrost which would otherwise occur due to the presence of saidheated member.
 3. A method of maintaining the temperature of a memberbelow that of its adjacent earthen support where said earthen support issubject to cyclical climatic temperature variations, comprising thesteps of locating an insulation layer and a thermocell between saidmember and earthen support each that the insulation layer is adjacentsaid member, selecting a heat sink fluid for said thermocell having afreezing point below that of the earthen support, providing saidthermocell with sufficient capacity to avoid changes in its temperaturewhen exposed to the cyclical climatic temperature variations of theearthen support, and selecting said insulation layer so as to reducesubstantially the effect of the temperature differential between saidthermocell and said member.
 4. The method of claim 3 wherein aninsulation layer is located between the thermocell and the earthensupport to minimize the heat flow therebetween.